(535b) Probing the Structure of High Viscosity Complex Fluids at High Shear Rates

Industrial applications, such as lubrication, mixing, spraying and injection, involve the flow of complex fluids at extreme deformation rates. Clogging, fluid degradation, and other processing challenges can arise in these extreme contexts and are often driven by structural changes in the fluid. Previous work has demonstrated that small angle neutron scattering used in conjunction with a microfluidic slit rheometer can be used to gather structural and rheological information about complex fluids. Additionally, data analysis isolates the scattering from the high-shear region located near the wall of the microfluidic channel, resolving shear-rate dependent scattering that is directly comparable to data gathered using the well-established technique of RheoSANS. The slit rheometer SANS cell (referred to as µRheoSANS) allows us to probe higher shear rates than those achieved in traditional RheoSANS experiments. However, only fluids with relatively low viscosities (η_∞ < 5 mPa∙s) are suitable for use with the prototype device used previously.

The work presented here will cover recent efforts to improve µRheoSANS, by incorporating a new syringe pump and more robust cell design that increases the maximum pressure the system can tolerate from 3 bar to 350 bar. The new device will enable investigations of a broad class of viscoelastic fluids, including paints, fracturing fluids, polishing slurries, lubricants, microemulsions, liquid crystals, and polymer melts. The new system will also be able to investigate effects of hydrostatic pressure head and temperatures (eventually up to 200°C) on the flow behavior of complex fluids. We will validate the new design by measuring a mildly viscoelastic wormlike micelle solution and comparing to previous experiments completed using the prototype device and Couette RheoSANS. Then, we will investigate a model rigid-rod dispersion, an aqueous suspension of cellulosic nanocrystals, using neutrons to directly probe the fluid structure and correlate structural transitions such as alignment, log-rolling, or wagging with the non-linear rheological behavior of the system.